For detecting the presence of such microorganism in food as Escherichia coli, Staphylococcus aureus, Vibrio or the like, that causes food poisoning, food manufacturing companies work on microbial detection. To express a level of contamination, number of living organisms per 1 g or 1 ml in foodstuff is used as an indicator when microbial detection is performed. Standard Methods Agar is widely used in the determination of microbial counts, being incubated at 35° C.±1° C. for 24 or 48 hours. To determine microbial counts, colonies on an agar plate are counted while viewing the agar plate or a colony counter is used for counting. In count methods, a dilution of the sample is mixed in a sterile dish with melted agar and colonies in a medium are counted after the agar is incubated.
Other approaches to the microbial detection method and system are taught in such Japanese Patent applications as 5-288992 and 10-240950. Such patent applications teach the way to detect microorganisms by processing image data collected with CCD camera, magnifying microorganisms with lenses.
However, traditional approach to the microbial counts have involved longer incubation duration since a colony has to be large enough to be counted visually, and a longer incubation often causes colony overlapping and count difficulty or inaccuracy problem when the contamination level in a sample is high. The method and system taught in Japanese Patent applications as 5-288992 and 10-240950 use lenses to magnify microorganisms so that focussing process is required and only the microorganisms at focal distance can be observed with the technique. The objective of the present invention is to resolve said problems and to provide a method for observing microscopic object by projection, a novel microbial detection method capable of more rapidly determining the presence and quantities of microorganisms accurately and easily, and a projection detecting system capable of facilitating precise microbial detection.